"Google has released an early version of Dart, a new programming language designed to take some of the pain out of developing applications for the Web. But while it's an evolutionary improvement on JavaScript, Dart faces a hard uphill battle for acceptance."

I think the point is that you will then run the output of Dart through the Google Closure compiler. In that way all the extra cruft is stripped out.

ClojureScript does the same thing. A stock "unoptimzied" "Hello World" is pages and pages of standard library functions, but it is also designed to run through the Google Closure (no j in this case) compiler and have all the dead code removed. After that, you're left with a very compact optimized file.